It is common in the industry to use plywood to construct forms in which to pour cement to allow for setting and curing into very specific shapes and dimensions.
In the concrete industry, it is desirable that the form boards which are used to mold the concrete until it has set, exhibit certain characteristics as follows: adhesion of the laminate to the board, ease of release of cement from the form, and durability of the laminate. If damage were to result to the finish of the concrete, it might become necessary to refinish the cement surface. This is a task which requires additional materials and time-consuming labor. If the form board is damaged significantly, it cannot be re-used.
There are different methods in the art on how to provide improved, re-usable form boards. However, ordinary plywood, usually treated on the surface with paraffin oil or in other ways and with a variety of mold release agents, is still being used most frequently. More sophisticated concrete form boards may be made by treating fir plywood with a penetrating coating of an epoxy resin followed by a polyurethane coating. These two coatings are fused and cured under thermosetting conditions. The epoxy/urethane resin coatings are, however, difficult to apply and still require the application of a release agent.
Alternatively, a phenolic resin impregnated paper overlay may be bonded to one side of a plywood panel. This overlay allegedly tends to bridge the gaps and cracks which would normally occur and have reasonably low water penetration.
Another alternative is to laminate a polyolefin film to the surface of the panel as disclosed in CA 919,896 and CA 931,486. However, the adhesion of the polyolefin to the panel is not good. Therefore, it is necessary to apply a primer to the panel before laminating the polyolefin to the primed surface to increase the adhesion properties. This is a long, difficult process.
The home construction industry commonly uses softwood plywood coated with release agents such as mineral oil for these cement forms. The disadvantage of this method is that the forms can generally only be re-used once or twice.
U.S. Pat. No. 4,352,925 discloses the use of copolyester compositions as heat-resistant adhesive compositions for use on various types of paper, paperboard, plastic, leather, metal, wood, ceramics, etc. However, it does not show the use of the copolyester compositions in a film comprising a polyolefin layer and a copolyester layer as does the present invention.
It would be advantageous to have more durable cement forms which exhibit excellent release properties and excellent resistance to delamination, since the commercial and industrial construction industries prefer to get many uses out of each set of cement forms for economic and convenience purposes.
It also would be advantageous to have a film used to produce cement forms wherein film can be applied to a wooden substrate without the necessity of applying a primer to the substrate before the application of the film.